(1) Field of the Invention
This invention relates to a microwave integrated circuit device in which a waveguide and a microwave integrated circuit (hereinbelow, abbreviated to "MIC") including a strip line etc. are made integral and which is small in size, low in cost and high in reliability.
(2) Description of the Prior Art
Devices exploiting the Doppler effect are known as a vehicular speed sensor (or speedometer) to be disposed on an automobile and as an apparatus for detecting a moving object.
From the viewpoint of size, cost and reliability, the devices are constructed by combining a waveguide and a MIC.
In the device hitherto proposed, in order to connect the waveguide circuit to the MIC composed of a strip line etc., there has been attempted an expedient wherein the MIC is provided with a coaxial connector and the waveguide is connected thereto through a separate coaxial waveguide adapter, or an expedient wherein an antenna pattern is formed on the front surface of a MIC plate, a conductor on the rear surface is taken off and inserted into the waveguide and a micro strip line on the plate is directly changed into the waveguide. With such expedients, however, the insertion loss of the circuit increases to degrade characteristics thereof. Further disadvantages are that the attachment or detachment of the MIC to or from the waveguide is troublesome and that the cost of the whole device becomes high. In order to eliminate such disadvantages and to make the MIC device easy in the attachment and detachment, excellent in airtightness and low in cost, the inventors have proposed a MIC device in which a MIC is mounted on a short-circuited plane within a waveguide. In this device, however, a solid-state element such as semiconductor diode and transistor, especially a mixer diode in the case of using the device as a receiving device is situated in close proximity to the short-circuited plane of the waveguide, so that the coupling between the solid-state element and an electrostatic field is liable to become insufficient. This leads to the disadvantage that the sensitivity of the microwave circuit device cannot be made sufficiently high.